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deno eval
deno eval executes a string of code directly from the command line without
needing a file. Unlike deno run, deno eval runs with all permissions
enabled by default.
Basic usage Jump to heading
deno eval "console.log('Hello from Deno')"
TypeScript works out of the box:
deno eval "const greeting: string = 'Hello'; console.log(greeting)"
CommonJS and ESM auto-detection Jump to heading
Starting in Deno 2.8, deno eval defaults to ESM but switches to CommonJS when
the snippet looks like a CJS script. A snippet is treated as CJS only when it
has no import / export declarations and it references one of the
CommonJS-specific bindings: require(, module.exports, exports.,
__dirname, or __filename. Anything else — including plain expressions — runs
as ESM, matching the longstanding deno eval default.
# Detected as CommonJS — uses require()
deno eval "const path = require('path'); console.log(path.join('a', 'b'))"
# Runs as ESM (the default) — no CJS-specific patterns
deno eval "console.log(1 + 2)"
# Runs as ESM because of the static import
deno eval "import { ok } from 'node:assert'; ok(true); console.log('ok')"
If the heuristic gets it wrong — for example when a snippet mentions require
only inside a string — pass --ext=mjs to force ESM or --ext=cjs to force
CommonJS.
Printing expression results Jump to heading
Use --print (or -p) to evaluate an expression and print its result, similar
to node -p:
deno eval -p "1 + 2"
# 3
deno eval -p "Deno.version"
# { deno: "2.x.x", v8: "...", typescript: "..." }
Reading from stdin Jump to heading
Combine with piped input for quick data processing:
echo '{"name":"deno"}' | deno eval -p "
const text = await new Response(Deno.stdin.readable).text();
JSON.parse(text).name
"
evalEvaluate a script from the command line
Options Jump to heading
--cached-onlyRequire that remote dependencies are already cached.
--certLoad certificate authority from PEM encoded file.
--checkEnable type-checking. This subcommand does not type-check by default; pass --check=all to also type-check remote modules. Alternatively, use the 'deno check' subcommand.
Use this argument to specify custom conditions for npm package exports. You can also use DENO_CONDITIONS env var. .
Configure different aspects of deno including TypeScript, linting, and code formatting.
Typically the configuration file will be called deno.json or deno.jsonc and
automatically detected; in that case this flag is not necessary.
--env-fileLoad environment variables from local file Only the first environment variable with a given key is used. Existing process environment variables are not overwritten, so if variables with the same names already exist in the environment, their values will be preserved. Where multiple declarations for the same environment variable exist in your .env file, the first one encountered is applied. This is determined by the order of the files you pass as arguments.
--extSet content type of the supplied file.
--frozen-lockfileError out if lockfile is out of date.
Load import map file from local file or remote URL.
--inspectActivate inspector on host:port [default: 127.0.0.1:9229]. Host and port are optional. Using port 0 will assign a random free port.
--inspect-brkActivate inspector on host:port, wait for debugger to connect and break at the start of user script.
--inspect-publish-uid--inspect-waitActivate inspector on host:port and wait for debugger to connect before running user code.
--locationValue of globalThis.location used by some web APIs.
--lockCheck the specified lock file. (If value is not provided, defaults to "./deno.lock").
--min-dep-age(Unstable) The age in minutes, ISO-8601 duration or RFC3339 absolute timestamp (e.g. '120' for two hours, 'P2D' for two days, '2025-09-16' for cutoff date, '2025-09-16T12:00:00+00:00' for cutoff time, '0' to disable).
--no-checkSkip type-checking. If the value of "remote" is supplied, diagnostic errors from remote modules will be ignored.
--no-configDisable automatic loading of the configuration file.
--no-lockDisable auto discovery of the lock file.
--no-npmDo not resolve npm modules.
--no-remoteDo not resolve remote modules.
--node-modules-dirSelects the node_modules directory mode for npm packages (not a path). One of: auto (create a local node_modules directory and install npm packages into it), manual (use the existing local node_modules directory, do not modify it), none (do not use a local node_modules directory; resolve npm packages from the global cache). Defaults to auto when the flag is passed without a value.
--node-modules-linkerSets the linker mode for npm packages (isolated or hoisted).
--preloadA list of files that will be executed before the main module.
--print, -pprint result to stdout.
--reload, -rReload source code cache (recompile TypeScript). With no value, reloads everything. Pass a comma-separated list of specifiers to reload only those modules; npm: reloads all npm modules; npm:chalk reloads a single npm module; jsr:@std/http/file-server,jsr:@std/assert/assert-equals reloads specific modules.
--requireA list of CommonJS modules that will be executed before the main module.
--seedSet the random number generator seed.
--unsafely-ignore-certificate-errorsDANGER: Disables verification of TLS certificates.
--v8-flagsTo see a list of all available flags use --v8-flags=--help
Flags can also be set via the DENO_V8_FLAGS environment variable.
Any flags set with this flag are appended after the DENO_V8_FLAGS environment variable.
--vendorToggles local vendor folder usage for remote modules and a node_modules folder for npm packages.
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